Mark Shea has this great piece in today's National Catholic Register on purity and the apostolic calling of the laity to the world.

"Beyond this, though, there is another dimension to holiness that has to be learned and many Catholics never do.

It is the realization that we do indeed live under the New Covenant and that our primary mission as Catholics is to make the world holy, not to keep the world from defiling us. We have to learn that the Church ultimately has the upper hand against sin because we have the power of Christ.

Some Catholics really don’t get this. To illustrate, let me quote a Catholic who was participating in a recent online discussion concerning whether Harry Potter books were proper for a Catholic to read: “One drop of anything not authentically Catholic poisons the whole glass.”

Now, this is not a column about Harry Potter. So let’s restrain the urge to go there. This is a column about purity. And the fact is, it is false to say that “One drop of anything not authentically Catholic poisons the whole glass.”

And this has ever been the Church’s approach. Everything from Stagecoach to 2001: A Space Odyssey is championed by the Vatican as good films without the slightest sense that, because they are the products of decidedly non-saintly Catholics or unbelievers, they are therefore necessarily “poison.”

The basic principle we have from the New Testament is that the power of the Spirit can overcome the powers of sin, hell and death. It is what has ordered the Church’s missionary work since the beginning. That is the meaning of the strange Dominical saying preserved at the end of the Gospel of Mark:

“And these signs will accompany those who believe: In my name they will cast out demons; they will speak in new tongues; they will pick up serpents, and if they drink any deadly thing, it will not hurt them; they will lay their hands on the sick, and they will recover” (Mark 16:17-18).

This language is particularly apt, particularly given the language we just saw above. The funny thing about the Gospel is how often, in the history of the Church, the Church has fulfilled Jesus’ promise, “If they drink any deadly thing, it will not harm them” (Mark 16:18).

The Church has drunk from all sorts of pagan wells, ranging from Plato and Aristotle to the various ways in which Norse, German, Druidic, Roman, Indian and other forms of pagan culture have been baptized and turned to the service of Christ."